As is the case with several bacterial pathogens of mammals, many plant pathogenic bacteria inject proteins into the host cell cytoplasm. Plant recognition of bacterial attack results in a defense response mediated by at least three defense signaling pathways. To test whether additional plant defense signaling pathways exist, I will identify genes that participate in these pathways. I will use whole genome microarray analysis to identify Arabidopsis thaliana genes that are induced in response to the bacterial pathogen Pseudomonas syringae but are triggered independently of the canonical defense signaling pathways involving salicylic acid, jasmonic acid and ethylene. I will perform mutational analysis of 192 of these genes to identify those genes that are likely to participate in novel disease signaling pathways that are required for plant defense against bacterial pathogens. I will study the role of these pathways in plant protection against pathogens with diverse colonization strategies. Further, I will detail how these pathways are triggered, how they function, and how they are organized. As these studies will identify novel plant signaling pathways that are required for disease resistance, they are crucial to the study of the plant immune response to microbial attack.